The invention relates to an apparatus and a method for reproducing a video signal recorded on a magnetic tape using a bandwidth compression technique known as "frequency folding".
Recently, along with the development in digital picture processing techniques, there have been improvements of the resolution in the direction parallel to scan lines of video-tape-recorded images played back using conventional magnetic recording/playback apparatus. The luminance signal resolution is generally degraded by the limited recording bandwidth of the conventional household magnetic recording and playback machines such as a video cassette recorder (VCR) or a video tape recorder (VTR), owing to performance limitations of the recording/playback head and the tape. Accordingly, an improved VHS system called a super VHS (S-VHS) system was introduced, wherein improved image quality is secured by recording the video signal at full bandwidth using a frequency-modulated carrier wave that is higher than that used for standard VHS recording. An S-VHS recording cannot be played back on a standard playback system because of the frequency-modulated carrier wave being higher than that used for standard VHS recording.
The specification and drawing of U.S. Pat. No. 5,113,262 issued to C. H. Strolle, C. B. Patel, W. F. Wedam, J. W. Ko, R. Scnitzler and J. K. Yun on May 12, 1992 and entitled "VIDEO SIGNAL RECORDING SYSTEM ENABLING LIMITED BANDWIDTH RECORDING AND PLAYBACK" is incorporated herein by reference. In the system described therein a bandwidth compression technique known as "frequency folding" is used to record a video signal at full bandwidth on a recording medium having a limited bandwidth, and then, the originally recorded composite video signal is reproduced through playback from the recording medium. The recording made by this new system can be played back on a standard reproducing system without undesirable artifacts accompanying reproduced picture.
However, the previous invention of the inventors and others claimed in U.S. Pat. No. 5,113,262 has a shortcoming. The quality of the reproduced image is degraded because some portions of signal are attenuated or have a phase error. Such degradation is caused by lack of phase-linearity in the analog portion of the playback system. This gives rise to departures from linear-phase operation, in which the group delay characteristic is not constant over all frequencies of interest, and interferes with the unfolding of the folded signal into the original full bandwidth.